Fabrics woven from polyamide filament yarns are predominately utilized in airbag manufacture due to the yarns' high energy absorption capability. This energy absorption capability is usually most easily defined as the area under the load-extension curve, and is most usually characterized by the yarn tensile index (defined as the yarn tenacity (cN/tex) times the square root of the elongation at break (%)). Energy absorption capability is particularly important due to the dynamic nature of the airbag deployment event, and previous work has been aimed at maximizing the energy absorption of polyester yarns to bring them closer to polyamides in properties.
The problem of improving the energy absorbing capability of polyester airbags has been addressed by increasing the tensile index of the polyester filament yarns used for weaving the fabrics used in the airbags. The process conditions used to manufacture these tougher yarns have been disclosed, using a high relax ratio after drawing the high tenacity yarn to increase the yarn elongation, and thus the toughness.
Airbag fabrics woven from such polyester filament yarns have failed in simulated deployment conditions. When airbag modules containing such fabrics woven from polyester filaments were preheated to about 80° C. or more, and then deployed, airbag seams pulled apart causing uncontrolled leakage of the inflator gas, a phenomenon known as fabric seam combing or fabric edge combing. These failures are not seen in airbags comprising fabrics woven from polyamide filament yarns.
In spite of attempts at solving seam combing problems, polyester airbags can still fail during a hot module deployment. In other testing of hot module deployment, the airbag module, which includes the inflator and folded airbag, was heated to 90° C. for about 4 hours prior to deployment and upon deployment the airbag failed. An exhaustive analysis of the failure mechanism in these tests indicated that failure was due to seam combing. The combined influences of inflation force, hot inflator gas, and the hot preconditioning, caused the polyester yarns at the fabric seam to stretch and to form gaps through which the gas escaped at an uncontrolled rate.
Therefore, a need exists for a woven polyester fabric that reduces the extent of seam combing in airbags and that exhibits similar characteristics as polyamide yarns when preconditioned to up to 100° C. and inflated under conditions of rapid heating and load.